Silver alloys



nited States Patent SILVER ALLGYS Charles L. Primrose, Nutley, N. J., assignor to The Ventore Corporation, Newark, N. J., a corporation of New Jersey No Drawing. Application August 30, 1955, Serial No. 531,589

Claims. (Cl. 75173) This invention relates to alloys and particularly to novel silver alloys and new and improved methods for their production.

By reason of its color and excellent electrical and thermal properties, silver is a very desirable metal for many applications. its use, however, is often restricted because of its inherently poor mechanical properties, and, in particular, its low tensile strength, hardness and elasticity. Much work has been done by industry in an attempt to develop silver alloys which, while retaining the desirable properties and characteristics of pure or relatively pure silver, would also present improved physical properties. Such alloys have not, however, proved entirely satisfactory. Often, when satisfactory characteristics such as tensile strength and elasticity have been obtained, the resulting alloy proves to be inferior with respect to color, thermal and electrical properties, or tarnish resistance.

It is an object of the present invention to provide new silver alloys having substantially the color of pure silver and other desirable inherent properties of silver, but which is characterized by markedly increased tensile strength, hardness, elasticity and resistance to tarnishing.

A further object of the invention is the provision of novel methods for producing homogeneous silver alloys possessing the aforementioned improved physical properties.

The alloys of the present invention comprise a major proportion of silver with smaller proportions of manganese,, copper, tin, zinc and nickel. I have found that the relative proportions in which these ingredients are employed within the alloys of my invention are critical, it being necessary to employ formulations within the following ranges in order to insure alloys possessing the improved properties hereinafter demonstrated with respect to my novel compositions:

Specifically, I have found that an alloy having the most advantageous properties is obtained in accordance with my invention when the final composition consists essentially of 4.00% by weight manganese, 2.64% by weight copper, 0.50% by weight tin, 0.17% by weight zinc and 0.17% by weight nickel, the balance consisting substantially entirely of silver (92.52%).

From the foregoing, it will be seen that the components of the alloy must be present in rather closely controlled amounts in order to avoid impairment of one or more of the desirable properties possessed by the preferred products of my invention. By reason of the fact that all of the metals involved except tin and zinc have relatively high melting points, and that tin melts at 232 C. while zinc melts at 420 C. and vaporizes at 907 C., it will be understood that it is difiicult to control the concentration of tin and zinc in such an alloy. This problem is further complicated by the fact that tin and zinc react with atmospheric components at relatively low temperatures. Still another problem is presented by the fact that whereas the alloy must be homogeneous as to all components, homogeneity as to zinc and tin is particularly diflicult to attain, because of the inherent physical properties of these elements.

The invention is based in part on my discovery that the aforementioned diificulties may be overcome by a unique procedure involving preparation of a pre-alloy of tin and zinc in a copper matrix, and thereafter uniformly mixing the pre-alloy with silver while in the molten state at a temperature not exceeding about 1000 C. The pre-alloy is prepared by heating 2.38-2.90 parts by weight copper to its melting point of 1083 C. under a reducing atmosphere and thereafter adding 0.45-0.55 part by Weight tin to the melt. When the tin is completely dissolved, the melt is cooled to 850-900 C., and 0.17-0.19 part by weight zinc is added, and the pre-alloy is permitted to cool and solidify as soon as the zinc has dissolved completely within the matrix.

The silver, amounting to 91.77-93.27 parts by weight, is then melted under an inert atmosphere and while in the molten state, at a temperature not exceeding 1000 C., 2.98-3.64 parts by weight of the copper-zinc-tin pre-alloy is added. When the resulting melt has become homogeneous, it is heated to a temperature not exceeding 1300 C., and 4.00-4.80 parts by weight manganese is added. This amount of manganese is sufficient to give an initial excess of 0.4 part by weight to compensate for manganese loss at the temperatures involved, so that the final manganese content of the alloy is 3.60-4.40 parts by weight. After homogeneity is again obtained, the melt is heated to a temperature not exceeding 1500 C., and 0.15-0.19 part by weight of nickel is added. This increased temperature is maintained until the melt is again homogeneous, and thereafter the melt is covered with sodium tetraborate, stirred vigorously and cooled. The slag is then removed and the alloy cleaned, remelted and cast into any desired shape.

The foregoing as well as other features and objects of the invention may be best understood by reference to the following specific examples of typical alloys prepared in accordance with my invention:

Example I 26.4 grams of copper were melted in a crucible under a reducing atmosphere maintained at a temperature of 1083 C. (melting point). To the molten copper 5.0 grams of tin were added and when the tin had completely dissolved, the temperature was reduced to 875 C. 1.7 grams of zinc were then added to the mixture, and, after the zinc had dissolved, the resulting pre-alloy was allowed to cool.

92.5 grams of silver were melted in a crucible under an inert atmosphere and the molten bath maintained at about 975 C. To the molten silver were added 3.31 grams of the copper-zinc-tin pre-alloy. The melt was allowed to become homogeneous and was then heated to 1250 C. With the melt at this temperature, 4.40 grams of manganese (a 0.40 gram excess to give 4.00 grams manganese in the final product) were added and the melt again allowed to become homogeneous. The melt Was then heated to 1475 C. and 0.17 gram of nickel was added. When the melt had become homogeneous, it was covered with sodium tetraborate and stirred vigorously.

The melt was then cooled, the slag removed and the alloy I cleaned, remelted and-cast into a test specimen.

Tested by standard procedures, the foregoing alloy possessed the following physical properties: a

that the superior strength, hardness and elasticity may be obtained without annealing and air hardening but these properties may be even further enhanced by such measures. I

The alloy of Example I is considered to be unusually advantageous because of its remarkable hardness, high tensile strength and improved resistance to tarnishing as stated hereinbefore. Even relatively small variations in the proportions recited in Example I will result in definite changes in these properties of the alloy, and, accordingly, the particular alloy illustrated by Example 'I is considered to be superior to those which may be prepared with other formulations within the operative alloying ranges hereinbefore set forth. As illustrated by the following additional examples, however, although other alloys prepared in accordance with the operative permissive ranges of my invention are inferior in certain respects to the alloy of Example I, they still present a definite improvement over conventional silver alloys.

Example 11 A pre-alloy was prepared in the same manner as ex- 40 plained in Example I, except 24.0 grams of copper, 1.5 grams of zinc and 4.5 grams of tin were employed. 93.15 grams of silver were melted as in Example I, and 3.0 grams of the pre-alloy incorporated therein. The procedure of Example I was then continued, using 4.1 grams of manganese and 0.15 gram of nickel. Subsequent tests demonstrated that the high-silver alloy thus produced did not possess the tensile strength of the alloy of Example I.

Example III A pre-alloy was prepared in the same manner as for Example I, except 28.0 grams of copper, 1.9 grams of zinc and 5.5 grams of tin were employed. 91.97 grams of silver were melted as in Example I, and 3.54 grams of the pre-alloy incorporated in the molten silver. The procedure of Example I Was then continued, using 4.7 grams of manganese and 0.19 gram of nickel. Again, the tensile strength of this alloy, as well as its tarnish resistant properties were somewhat inferior to the corresponding properties of the alloy prepared in accordance with the formulation of Example I.

Alloys produced in accordance with the invention may be shaped into ingots, bars, sheets, rods or Wires or otherwise worked or tooled in accordance with conventional procedures.

Since it is considered obvious that many changes and modifications can be made in the foregoing methods and procedures without departing from the nature and spirit of my invention, it is to be understood that the invention is not to be limited to the specific details oifered by way of illustration above, except as set forth in the following claims.

I claim:

1. An homogeneous silver alloy having substantially the color of pure silver, said alloy being characterized by improved tensile strength, hardness and elasticity, and' 7 being more resistant to'staining, corrosion, and tarmshing than is pure silver, comprising the following ingredients Within the ranges indicated based on percentages by weight:

Silver 91.77-93.27 Manganese 3.60-4.40 Copper 2.38-2.90 Tin 0.45-0.55 Zinc 0.l5.0.19 Nickel 0.15-0.19

2. An homogeneous silver alloy having substantially the color of pure silver, said alloy being characterized by improved tensile strength, hardness and elasticity, and being more resistant to staining, corrosion, and tarnishing than is pure silver, comprising 4.00% by weight manganese, 2.64% copper, 0.50% tin, 0.17% zinc and 0.17% nickel, the balance being silver.

3. A method for producing improved silver alloys comprising the steps of uniformly admixing with 91.77-93.27

parts by weight molten silver at a temperature not ex-' ceeding 1000 C., 2.98-3.64 parts by weight of an homogeneous pre-alloy consisting of 2.382.90% by weight copper, OAS-0.55% by weight tin and 0.150.19% by weight zinc, heating the resulting'melt to a temperature not exceeding 1300 C., uniformly admixing with the heated melt 4.00-4.80-parts'by weight manganese, heat ing the resulting melt to a temperature not exceeding 1500 C., uniformly admixing with the heated melt 0.15- 0.19 part by weight nickel, and cooling the melt to obtain an homogeneous silver alloy having substantially the color of silver and characterized by increased tensile strength, hardness, elasticity and resistance to tarnishing. 4. A method for producing improved silver alloys comprising the steps of preparing an homogeneous prealloy by heating 2.38-2.90 parts by Weight copperuntil" molten, incorporating 0.45-0.55 part by weight tin in the molten copper, cooling the melt to 850-900 C., and

incorporating 0.170.19 part by weight zinc in the cooled melt; uniformly mixing 2.98-3.64 parts by weight of.-

said pre-alloy and 91.77-93.27 parts by weight molten silver at a temperature not exceeding 1300" C. and uniforrnly mixing 4.004.80 parts by Weight manganese in the melt thus produced; heating the resulting melt to a temperature not exceeding 1500 C. and uniformly mix- 0 ing 0.15-0.19 part by Weight nickel in the melt thus produced; and cooling the melt to obtain an homogeneous silver alloy having substantially the color of silver and characterized by increased tensile strength, hardness,

elasticity and resistance to tarnishing.

5. A method for producing improved silver alloys containing relatively small proportions of tin and zincfsuch alloys being homogeneous as to all constituents and the constituents being present in the final alloy in accurately controlled amounts, comprising the steps of preparing a pre-alloy of tin and zinc in a copper matrix, and thereafter incorporating 2.98-3.64 parts by weight of said pre-alloy in 91.77-93.27 parts by weight of molten silver While maintaining the temperature of the silver at a value not exceeding 1000 C.

No references cited. 

1. AN HOMOGENEOUS SILVER ALLOY HAVING SUBSTANTIALLY THE COLOR OF PURE SILVER, SAID ALLOY BEING CHARACTERIZED BY IMPROVED TENSILE STRENGTH, HARDNESS AND ELASTICITY, AND BEING MORE RESISTANT TO STAINING, CORROSION, AND TARNISHING THAN IS PURE SILVER, COMPRISING THE FOLLOWING INGREDIENTS WITHIN THE RANGES INDICATED BASED ON PERCENTAGES BY WEIGHT: 